Solanum is a large and diverse genus of flowering plants, which include two food crops of the highest economic importance, the potato and the tomato. It also contains the nightshades and horsenettles, as well as numerous plants cultivated for their ornamental flowers and fruit.

The generic name was first used by Pliny the Elder (23-79) for a plant also known as strychnos, most likely S. nigrum. Its derivation is uncertain, possibly stemming from the Latin word sol, meaning "sun," referring to its status as a plant of the sun. Another possibility is that the root was solare, meaning "to soothe," or solamen, meaning "a comfort," which would refer to the soothing effects of the plant upon ingestion.[2]

The species usually, most commonly called nightshade in North America and Britain, is Solanum dulcamara, also called bittersweet or woody nightshade. Its foliage and egg-shaped red berries are poisonous, the active principle being solanine, which can cause convulsions and death if taken in large doses. The black nightshade (S. nigrum) is also generally considered poisonous, but its fully ripened fruit and foliage are cooked and eaten in some areas. The deadly nightshade (Atropa belladonna) is not in the Solanum genus, but is a member of the wider Solanaceae family.

Most parts of the plants, especially the green parts and unripe fruit, are poisonous to humans (although not necessarily to other animals), but many species in the genus bear some edible parts, such as fruits, leaves, or tubers. Three crops in particular have been bred and harvested for consumption by humans for centuries, and are now cultivated on a global scale:

The genus was established by Carl Linnaeus in 1753.[5] Its subdivision has always been problematic, but slowly some sort of consensus is being achieved.

The following list is a provisional lineup of the genus' traditional subdivisions, together with some notable species.[5] Many of the subgenera and sections might not be valid; they are used here provisionally as the phylogeny of this genus is not fully resolved yet and many species have not been reevaluated.

Cladistic analyses of DNA sequence data suggests that the present subdivisions and rankings are largely invalid. Far more subgenera would seem to warrant recognition, with Leptostemonum being the only one that can at present be clearly subdivided into sections. Notably, it includes as a major lineage several members of the traditional sections Cyphomandropsis and the old genus Cyphomandra.[1]